1. Field of the Invention
The present invention relates to a method for treatment of cataract which comprises administering a prostacyclin compound to a subject.
Prostacyclin is (called) another name of prostaglandin I.sub.2.
Prostaglandins (hereinafter, prostaglandins are referred to as PGs) are members of a class of organic carboxylic acid that are contained in human and most other mammalian tissues or organs and that exhibit a wide range of physiological activities. Naturally occurring PGs possess as a common structural feature the prostanoic acid skeleton: ##STR1## The PGs are classified based on the structural feature of five-membered ring moiety into PGAs, PGBs, PGCs, PGDs, PGEs, PGFs, PGGs, PGHs and PGJs, while PGIs have an different skeleton, shown below, formed by cyclization between the .alpha.-chain and the five-membered ring. ##STR2## Some of synthetic analogues have somewhat modified skeletons. These are further classified based on the presence or absence of unsaturation and oxidation in the chain moiety as:
Subscript 1--13,14-unsaturated-15-OH PA0 Subscript 2--5,6- and 13,14-diunsaturated-15-OH PA0 Subscript 3--5,6- 13,14- and 17,18- triunsaturated-15-OH
2. Background Information
Natural PGI.sub.2 is known to have an action of inhibiting platelet aggregation and hypotensive activity. Further, carbacyclin (also known as 9(0)-methanoprostacyclin or 9(O)-methano-PGI.sub.2), which is a synthetic PG derivative having a methylene group in place of the oxygen at position 6a(9.alpha.) of PGI.sub.2, is known to have an action of inhibiting platelet aggregation. Also, compound having a nitrogen in place of the oxygen at position 6a(9.alpha.) and a sulfur in place of the methylene at position 5 of PGI.sub.2 (i.e. 9-deoxy-9.alpha.,6-nitrilo-5-thia-PGF.sub.1.alpha.) is known. However, it has not been reported that prostacyclin compounds have an activity useful in treatment of cataract.
As a result of extensive studies about the biological properties of compounds having natural and synthetic prostacyclin, the present inventor has discovered that these compounds are useful as an agent for treating cataract.